allow to publish channel labels instead of channel ids.

[MaxineMuster]

• introduce a new "bit-vector" g_PublishChannelLabel (like e.g. g_doNotPublishChannels) which needs to be 1 to publish the label instead of the channel
• as a quick hack I "extended" the SetChannelLabel command: it uses 0/1 to show/hide the prefix "Toggle". Now you can use 2/3 to do the same, but use labels as topic. (so instead of calling "SetChannelLabel 30 MeinDimmer 0" you may call "SetChannelLabel 30 MeinDimmer 2" (and "3" instead of "1" to hide the prefix)
• I also tried to do the proposed change in hass.c, but I'm not sure, if that's the only part of code which needs adjustments...
• If label shall be published, the label will be "validated", unwanted characters are set to '_'.